1. Field of the Invention
The present invention relates to a dielectric ceramic composition having resistance to reduction and an electronic device comprising the dielectric ceramic composition in a dielectric layer, and further specifically, relates to a dielectric ceramic composition with high rated voltage (e.g. 100V or more), preferable to use in mid-high voltage applications, and electronic device.
2. Description of the Related Art
A multilayer ceramic capacitor, an example of electronic devices, for example, is manufactured by firing a green chip obtained by stacking alternately ceramic green sheets comprising pre-determined dielectric ceramic composition and internal electrode layers in a pre-determined pattern to be integrated. Since the internal electrode layer of multilayer ceramic capacitor is integrated with the ceramic dielectric body by firing, a material not reacted with the ceramic dielectric body needs to be selected. Therefore, as a material constituting the internal electrode layer, there has been no choice but using expensive noble metal such as platinum and palladium.
However, dielectric ceramic composition wherein inexpensive base metal such as nickel and copper can be used has been recently developed to attain significant cost reduction.
Also, with more densified electronic circuit, it is highly demanded to downsize an electronic device, and more downsized multilayer ceramic capacitors with higher capacitance are rapidly developed. A dielectric layer in a multilayer ceramic capacitor are becoming thinner, and a dielectric ceramic composition is required to maintain the reliability of a capacitor even when making it thinner. Especially when downsizing and increasing capacitance of a mid-high-voltage capacitor used at high rated voltage (e.g. 100V or more), a highly-reliable dielectric ceramic composition is required to constitute a dielectric layer.
To address it, for example, the Japanese Patent Publication 3567759 discloses a dielectric ceramic composition for a capacitor used under high frequency wave and high voltage, comprising a compound as a main component expressed by a composition formula, ABO3+aR+bM (note that ABO3 is barium titanate based solid solution; R is an oxide of metal element such as La; and M is an oxide of metal element such as Mn), and a sintering auxiliary agent including at least one element from B element and Si element as subcomponent.
The Japanese Patent Publication 3567759 also describes that XZrO3 (note that X is at least a metal element selected from Ba, Sr and Ca) as an additive component of the main component is added in a concentration of 0.35 mole or less with respect to 1 mole of barium titanate based solid solution expressed by ABO3 of the main component.
However, a dielectric ceramic composition according to the Japanese Patent Publication 3567759 is low in withstand pressure (breakdown voltage) and insufficient in lifetime characteristics (accelerated lifetime of insulation resistance), resulting in a problem of lowering reliability. Especially, the problem is more significant when downsizing and increasing capacitance of a multilayer ceramic capacitor. Therefore, to attain downsizing and increase in capacitance, it has been desired to improve withstand pressure and lifetime characteristics (accelerated lifetime of insulation resistance).